CVE-2026-35040

The record

fast-jwt provides fast JSON Web Token (JWT) implementation. Prior to 6.2.1, using certain modifiers on RegExp objects in the allowedAud, allowedIss, allowedSub, allowedJti, or allowedNonce options in verify functions can cause certain unintended behaviours. This is because some modifiers are stateful and will cause failures in every second verification attempt regardless of the validity of the token provided. Such modifiers are /g (global matching) and /y (sticky matching). This does NOT allow invalid tokens to be accepted, only for valid tokens to be improperly rejected in some configurations. Instead it causes 50% of valid authentication requests to fail in an alternating pattern. This vulnerability is fixed in 6.2.1.

Affected packages

Related vulnerabilities

• GHSA-3j8v-cgw4-2g6q fast-jwt: Stateful RegExp (/g or /y) causes non-deterministic allowed-claim validation… Same vulnerability
• CVE-2026-44351 fast-jwt provides fast JSON Web Token (JWT) implementation. Also affects fast-jwt
• GHSA-gmvf-9v4p-v8jc fast-jwt: JWT auth bypass due to empty HMAC secret accepted by async key resolver Also affects fast-jwt
• GHSA-cjw9-ghj4-fwxf fast-jwt has a ReDoS when using RegExp in allowed* leading to CPU exhaustion during token… Also affects fast-jwt
• CVE-2026-35041 fast-jwt provides fast JSON Web Token (JWT) implementation. Also affects fast-jwt
• CVE-2026-35039 fast-jwt provides fast JSON Web Token (JWT) implementation. Also affects fast-jwt
• CVE-2026-35042 fast-jwt provides fast JSON Web Token (JWT) implementation. Also affects fast-jwt
• CVE-2026-34950 fast-jwt provides fast JSON Web Token (JWT) implementation. Also affects fast-jwt